1. Field of the Invention
The present invention relates in general to electronic circuits and in particular to circuits and methods for controlling transients during audio device power-up and power-down, and systems using the same.
2. Description of the Related Art
Purchasers of state of the art home and portable audio systems expect improved audio performance, as well as more options for controlling playback from the given recording media. One of the most important performance criteria is the elimination of clicks, pops, noise and other artifacts audible to the user. Not only are these audible artifacts distracting to the listener, but they can also damage the system speakers or headset, This is especially true with transient artifacts, such as clicks and pops, which may spike the output signal driving the speakers or headset to a relatively high level.
In a typical audio system, the loads (e.g., the speakers or headset) are AC coupled to an audio integrated circuit sourcing electrical analog audio signals through a coupling capacitor. The normal quiescent output node voltage is roughly xc2xd of the power supply voltage. However, before power is supplied to the circuit, the output node voltage at the coupling capacitors is zero volts. Subsequently, when the circuit is powered-up, the output node voltage transitions from zero volts to the quiescent voltage, thereby charging the coupling capacitors. This voltage transition can generate an audible sound in the speakers or headset, typically called a xe2x80x9cpop.xe2x80x9d A xe2x80x9cpopxe2x80x9d can also occur when the system powers down and when the output nodes transition from quiescent voltage to zero volts.
While there are presently a number of different of techniques for controlling pops, these techniques adversely impact other aspects of system performance. Consequently, new circuits and methods are needed which control pops without significantly impacting other aspects of system performance.
According to one embodiment of the inventive concepts circuitry is disclosed for ramping a voltage across a load. Charging circuitry charges a capacitor to generate a ramp-up wave form. Circuitry is also included for selectively decoupling a first driver from the load during a ramping up mode and coupling the first driver to the load during a normal operating mode. A ramp-up driver is selectively coupled to the load during the ramp-up mode which ramps up the voltage across load in response to the ramp-up wave form generated by the charging circuitry.
The principles of the present invention also provide for the ramping down of voltage across an output load. A capacitor is precharged to a selected voltage and a discharge circuit discharges the capacitor to generate a ramp-down wave form. Circuitry is also provided for selectively decoupling a first driver from output load during the ramping down of the voltage across output load. A ramp-down driver selectively ramps-down the voltage across output load in response to the ramp-down wave form generated by discharge circuit.
The inventive concepts allow for the control transients appearing to an output load during device power-up and power-down. These concepts are particularly useful in audio applications for eliminating or minimizing audible xe2x80x9cpopsxe2x80x9d in an audio system, although not necessarily limited thereto.